We know that three phase power supply is a very efficient way to supply power. Most of the industrial purpose three phase power is supplied. But sometimes industry need a high power DC supply to drive some special device like trolley buses, cranes etc.
So, we need to rectify the three phase AC power supply to DC.
There are mainly two methods of three phase full wave rectification 1. Three phase full wave uncontrolled bridge rectifier and 2. Full wave control rectifier.
Three phase full wave uncontrolled bridge-
The uncontrolled version of three phase full wave bridge rectifier can be constructer by connecting by connecting six diodes in bridge configuration across the three phase AC power supply.
Look the picture carefully
Six diodes rectifies the three phase power supply then a large capacitor is used at the bridge output terminals across the load in order to minimize the ripple contents in the wave across the load. This in turn results in a constant output voltage which is pulsating DC in nature.
Three phase full wave controlled bridge rectifier-
The main disadvantage of uncontrolled rectifier is that it’s output voltage can not be control without controlling the input voltage. To overcome this problem we use . Full wave control rectifier
This version of rectifier can be constructed by using control devices such as thyristors in place of diodes.
This type of rectifier can be classified into two categories 1. Full wave half controlled rectifier 2. Full wave fully controlled rectifier
For diode rectification when the power demand is high than power diodes( 16FMR. 16A,600V PIV) must be used. As the diodes are oh high current rating, proper heat sinks will have to be used for heat dissipation. The Indian market price of these type of power diodes is near about 45 for each.